1. Field of the Invention
The present invention relates generally to a valve with a reduced number of exhaust ports and vents and, more particularly, to a pilot operated valve which eliminates the pilot vent, the piston cavity vent and one of two exhaust ports.
2. Description of the Prior Art
As will be described in greater detail in conjunction with FIG. 1, spool valves require vents and exhaust ports in order to operate properly when made in accordance with known techniques. If the spool valve is operated by a pilot valve, the pilot cylinder must also be provided with a vent.
In operation, the vents and exhaust ports create a significant problem in certain applications. For example, if the pilot operated spool valve is enclosed in a cabinet with electronic or electromechanical equipment, the venting of the valve within the cabinet structure can cause damage to the electrical equipment. Another problem that relates to the use of a pilot operated spool valve occurs when one or more of the vents becomes restricted. This restriction can occur because of the accumulation of dirt in the vent, the existence of an insect nest in the vent conduit or the obstruction of the vent conduit by frozen liquid. If a vent is plugged for any reason, the operation of the value is seriously impaired and a catastrophic failure can occur. The present invention minimizes the number of exhaust or vent openings of a pilot operated spool valve in several ways.